In a conventional automatic transmission drivetrain, a torque converter is located between the crankshaft of an internal combustion engine and a multiple speed ratio transmission. The torque converter functions to provide fluidic coupling of the engine output to the driveline generally at low vehicle speeds (higher transmission speed ratios). Vehicle launch performance is enhanced by the torque converter's torque multiplication effects. And, the fluidic coupling of the torque converter also provides effective decoupling of engine torque pulsations to the driveline and, perhaps more significantly, damping of driveline torsional disturbances back to the engine. Generally at higher vehicle speeds (i.e. lower transmission speed ratios) and light throttle, the fluidic coupling of the torque converter may be replaced with the direct mechanical coupling of the engine to the driveline via a torque converter clutch (TCC). The output side of the TCC typically includes damping springs to attenuate the effects of the periodic torque pulsations occasioned by the cylinder events of the internal combustion engine on the driveline and any driveline disturbances back to the engine.
Torque converters have inherent efficiency shortfalls as some portion of the input energy is lost to the fluid. It is known to control the TCC at higher speed ratios and at points in a driving cycle normally reserved for fluidic coupling by the torque converter. Such early TCC control is additionally distinguished from conventional TCC lock-up, however, in that a slip is maintained across the TCC to provide some damping and isolation between the engine and the driveline. Such control may be generally referred to as controlled capacity TCC control.
While the torque converter achieves many vehicle performance and driveline isolation objectives commendably, it is recognized that the fluidic losses of such devices suggests opportunity for improving vehicle efficiency. While controlled capacity TCC improves upon the fluidic losses of the torque converter, fluid losses still remain as does the substantial hardware and mass—including substantial fluid mass associated with necessary coupling fluid—associated with a torque converter and TCC complement.
So called starting clutches have been proposed for replacing the torque converter. In essence, starting clutches have been proposed to effect many of the benefits of the torque converter clutch during vehicle launches without being encumbered by the fluidic losses associated therewith. Additionally, many of the benefits of a controlled capacity TCC are believed possible by employing such a starting clutch without many of the hardware and mass penalties associated with a torque converter and TCC complement. However, the inherent damping characteristics (or lack thereof) associated with starting clutches are substantially less ideal than those of the fluidic coupling of the torque converter and present significant challenges to attaining acceptable levels of driveline disturbance in such a system.